The present invention relates to a circuit arrangement for signal mixing, and relates particularly to a circuit arrangement for mixing an input signal with at least one carrier signal.
Conventional mixer circuits mix or multiply an audio-frequency, digitally encoded baseband signal with a radio-frequency carrier signal. Such mixer circuits should exhibit a high level of linearity, a high level of common-mode rejection in the baseband signal, low noise and the lowest possible power consumption. In addition, it is desirable to be able to operate a mixer circuit over a broad frequency range. In the case of conventional mixer circuits, a distinction is drawn between “single-balanced” and “double-balanced” mixers. When a mixer receives a differential carrier signal (LO signal) while the signal to be mixed is single-ended, this mixer is referred to as “single-balanced”. When both the carrier signal and the signal to be mixed are of differential design and are supplied to the mixer in differential form, such a mixer is referred to as a “double-balanced” mixer.
A fundamental drawback of the conventional circuit arrangement is the high power consumption of the mixer circuit for setting the operating point when a resistor is used as a load element. If the quiescent current is too low, common-mode components and hence unwanted nonlinearities in the subsequent amplifier stages arise at a high level of signal modulation on the load resistor. The use of coils as a load element results in a reduction in the quiescent current and in the common-mode components, but means that a larger area is used up and that the transfer characteristic of the mixer circuit is frequency dependent.
For these and other reasons, there is a need for the present invention.